By Danielle Torrent
Did an ancient crocodile relative give the world’s largest snake a run for its money? In the post-dinosaur world of giants, Florida Museum of Natural History researchers discovered a new species related to crocodiles they say ate the same freshwater fish as Titanoboa.
Sixty-five million years ago, when a mass extinction wiped out dinosaurs, flying reptiles, large swimming reptiles and many other marine animals, few survivors were left to tell the story.
But University of Florida researchers recently unearthed the second member of a family that lived alongside the beasts, yet mysteriously survived the theorized asteroid strike that forever changed the atmosphere of the world.
“The same thing that snuffed out the dinosaurs killed off most of the crocodiles that were alive at the time,” said Florida Museum of Natural History graduate student Alex Hastings, lead author of a study describing the new species of dyrosaurid published Sept. 15, 2011, in Palaeontology. “The dyrosaurids are one of the few groups to survive the extinction and later become more successful.”
The 60-million-year-old freshwater relative to modern crocodiles is the first known land animal from the Paleocene New World Tropics specialized for eating fish, which was also part of the diet of the world’s largest snake.
“The younger individuals were definitely not safe from Titanoboa, but the biggest of these species would have been a bit much for the 42-foot snake to handle,” Hastings said.
Fossils of a partial skeleton of the 20-foot extinct species, Acherontisuchus guajiraensis, helps researchers better understand the diversity of animals that occupied the oldest known rainforest ecosystem, what is today northeastern Colombia. Commonly believed to be ocean-dwelling, coastal reptiles, the information challenges previous theories the animals only would have entered freshwater environments as babies before returning to sea.
As cold-blooded survivors of an ecological catastrophe and the appearance of new competitors, their evolution is intrinsically linked with the environment. By studying these changes, researchers may be able to better understand how animal life will respond to climate pressures in the future.
“We’re facing some serious ecological changes now,” said Christopher Brochu, an assistant professor of vertebrate paleontology in the department of geoscience at the University of Iowa, who was not involved in the study. “A lot of them have to do with climate and if we want to understand how living things are going to respond to changes in climate, we need to understand how they responded in the past. This is a really wonderful group for that because they managed to survive some catastrophes, but they seemed not to survive others and their diversity does seem to change along with these ecological signals.”
The species is the second ancient crocodyliform found in the Cerrejon mine of northeastern Colombia, one of the world’s largest open-pit coal mines. The excavations were led by study co-authors Jonathan Bloch, Florida Museum associate curator of vertebrate paleontology, and paleobotanist Carlos Jaramillo of the Smithsonian Tropical Research Institute.
Hastings began uncovering parts of the Acherontisuchus guajiraensis skeleton in 2007 and 2008, a tedious process whether the bones are large or small, he said.
“Because it’s so delicate, you really need to use small tools,” Hastings said. “So with something as large as these fossils, it takes a very long time to go over it – centimeter-by-centimeter – to clean it and reveal the features needed for research.”
The age of the fossils makes them brittle, and as they become exposed to the atmosphere, their likelihood of crumbling increases. In order to preserve as much fossilized bone as possible, researchers coat the specimens in glue that is later removed in the lab.
“You have to use so much glue just to keep it together, it just wants to crumble into dust as soon as you look at it,” Hastings said. “Once you’ve got it completely solid, you can start working away some of the glue you’ve added, as well as the dirt. It’s a very exhaustive, integrative process.”
But Hastings said in this case, the year-long preparation process was particularly rewarding since he unearthed the type specimens used to name and describe the new species in the study.
“It’s really satisfying to have not only been able to do the analysis and study the fossils, but to actually have collected them myself – you don’t always get that opportunity,” Hastings said. “It’s nice to have taken something from the field, brought it back, coaxed it out of the rock for a year – it’s got all your blood, sweat and tears in it – and actually have it formulate into a publication that other people can pick up and learn from. It’s really been a rewarding process for me.”
What bones can tell
During the Paleocene in South America, reptiles, including giant snakes, turtles and crocodiles, dominated the environment. The dyrosaurid family originated in Africa about 75 million years ago, toward the end of the age of dinosaurs, and arrived in South America by swimming across the Atlantic Ocean.
While previously believed to be coastal reptiles, the adult specimens found show dyrosaurids also evolved to adapt to freshwater environments, and the evidence can be seen in the bone structure.
“Parts of the pelvis have been really helpful in finding out how they move differently from other members of this family,” Hastings said. “The pelvis has muscle attachments that are actually used for breathing. They can control the shape of their lung cavity in order to control their position within the water.”
Other fossils of dyrosaurids found in Africa show adaptations for turbulent coastal environments, including larger bone structure to support larger muscles. The bones of the new species are reduced, representing life in a more placid environment.
“The general common wisdom was that ancestrally all crocodyliforms looked like a modern alligator, that all of these strange forms descended from a more generalized ancestor, but these guys are showing that sometimes one kind of specialized animal evolved from a very different specialized animal, not a generalized one,” Brochu said. “It’s really showing us a level of complexity to the history that 10 years ago was not anticipated.”
The ancient crocodile relative’s long, narrow jaw shows a specialization for hunting the lungfish and relatives of bonefish that inhabited the water.
“This one is related to a group that typically had these long snouts, but it hadn’t been found in this area before or especially for this time period, so it really fit in this missing window of time and space,” Hastings said. “It would have had a relatively similar diet to the other ones, but it lived in a much more freshwater environment, which is one of the more surprising things about this.”
Published on Science Stories: October 2011.